ClickHouse® cluster maintenance
Maintenance is a process that helps maintain the health and performance of your cluster.
Automatic installation of software updates and revisions (including stopped clusters)
Security and compliance settings deployment and evaluation
Other maintenance activities.
Changing the cluster's software version isn't a part of the maintenance procedures.
A maintenance window helps you track or set a schedule for the maintenance activities on your managed clusters.
In Managed Service for ClickHouse®, the maintenance procedure varies depending on the number of hosts on your cluster:
In single-host clusters, maintenance is performed on a single ClickHouse® host, which results in your cluster becoming unavailable until the procedures are complete.
If a host needs restarting during maintenance, it'll be unavailable until the restart is complete. If you access the cluster using the FQDN or IP address of the ClickHouse® host, such a cluster may become unavailable.
If a cluster consists of multiple shards, our Managed Service for ClickHouse® performs shard maintenance in parallel: first, the maintenance is performed on hosts of one shard, then two shards, four, and so on, up to ten.
This is what a step-by-step maintenance sequence looks like for a cluster with four shards (
D), three hosts each (
1: A1 2: A2 B1 3: A3 B2 C1 D1 4: B3 C2 D2 5: C3 D3
This sequence makes sure no shard becomes unresponsive during maintenance.
Host maintenance works the same as in clusters with a single shard. If you access the cluster shard using the FQDN or IP address of the ClickHouse® host, such a shard may become unavailable.